The present invention relates to perpendicular magnetic recording media, and more particularly relates to media in which noise is suppressed through the use of a laminated soft magnetic underlayer. The lamination controls the magnetic domain structure of the soft underlayer.
Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. An approach to perpendicular magnetic recording requires the use of recording media with a magnetically soft underlayer which provides a flux path from the trailing write pole to the leading return pole of the writer. The soft underlayer enables substantially stronger fields than can be generated with a ring head in conventional longitudinal recording systems. The soft underlayer also provides sharper field gradients which enable writing on high coercivity media. In addition, the soft underlayer helps during the read operation. During the read back process, the soft underlayer produces the image of magnetic charges in the magnetically hard layer, effectively increasing the magnetic flux coming from the media. This provides a higher playback signal.
One of the challenges of implementing perpendicular recording is to resolve the problem of soft underlayer noise. The noise is caused by fringing fields generated by magnetic domains, or uncompensated magnetic charges, in the soft underlayer that can be sensed by the reader. For the write process to be efficient, high moment materials, e.g., Bs greater than 20 kG, may be used for the soft underlayer. If the magnetic domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady-state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time-dependent noise. Both types of noise should be minimized.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
The present invention provides perpendicular magnetic recording media having a laminated soft magnetic underlayer which includes multiple layers that generate opposed magnetic fields in the soft magnetic underlayer. The laminated soft magnetic underlayer may be brought into a substantially single-domain state by the magnetic fields. Reducing or eliminating multiple domains addresses the noise problem noted above. In one embodiment, the magnetization is aligned radially in a direction substantially perpendicular to the recording tracks of a disk in order to reduce or eliminate local domain walls in the soft underlayer. It is noted that a xe2x80x9csingle-domainxe2x80x9d state is an approximation, which applies to materials without any magnetic defects. In actual magnetic films, the film may be magnetically saturated in accordance with the present invention in order to sufficiently reduce the number of domain walls, thus suppressing soft underlayer noise.
An aspect of the present invention is to provide a perpendicular magnetic recording medium including a hard magnetic recording layer and a soft magnetic underlayer. The underlayer comprises means for generating a noise-reducing magnetic field in the soft magnetic underlayer.
Another aspect of the present invention is to provide a laminated soft magnetic underlayer of a perpendicular magnetic recording medium. The laminated soft magnetic underlayer comprises first and second layers of magnetically soft material separated by a non-magnetic spacer layer.
A further aspect of the present invention is to provide a method of making a magnetically soft underlayer of a perpendicular magnetic recording disk. The method includes the steps of depositing a first magnetically soft layer on a substrate disk, depositing a non-magnetic spacer layer on the first magnetically soft layer, and depositing a second magnetically soft layer on the non-magnetic spacer layer. The arrangement of the magnetically soft layers and the non-magnetic spacer layer generates opposed magnetic fields in the soft magnetic underlayer.
These and other aspects of the present invention will be more apparent from the following description.